Burner for a gas combustor and a method of operating the burner thereof

ABSTRACT

A burner for a gas combustor and a method of operating the burner are disclosed. The burner includes a front surface area divided into a plurality of subareas and inlets arranged on the front surface area such that each subarea is encircled by at least four inlets and such that during operation of the burner, a gas recirculation in the combustor is facilitated corresponding to each subarea.

FIELD OF INVENTION

The present invention relates to a gas combustor burner particularlyarrangement of inlets in the burner which supplies combustible gas tothe combustor and its operation for fuel staging.

BACKGROUND OF INVENTION

Gas turbines are used to convert heat energy to mechanical energy, forexample in power plants. Gas turbines have combustion chambers in whicha fuel is burned with air. The combustion chambers of gas turbine plantsare supplied with liquid and/or gaseous fuel using burner consisting ofone or more nozzle or inlets. The burner can also be used to carry airrequired for the combustion. For the optimal operation of the gascompressors, stable flames should be formed in the combustion chamberduring combustion. Common techniques for flame stabilization include theformation of small eddies or recirculation zones in the combustionchamber. The temperature in the recirculation zone needs to be above athreshold especially at lower load conditions to sustain combustionwhich will result in stable operation.

A flame will be inherently unstable if the energy release from thecombustion is insufficient to raise the temperature to a level at whichcombustion is self sustaining under conditions of heat loss includingradiation to and from the flame and under hot gas recirculation. Theability to keep a sustainable temperature to maintain combustion atdifferent loads especially at lower loads and simultaneously achieveemission targets is a great challenge in gas turbine operations.

SUMMARY OF INVENTION

In view of the foregoing, an embodiment herein includes a burner for agas combustor. The burner comprises a front surface area divided into aplurality of subareas. Inlets are arranged on the front surface areasuch that each subarea is encircled by at least four inlets such thatduring operation of the burner, a gas recirculation in the combustor isfacilitated corresponding to each subarea.

In view of the foregoing, another embodiment herein includes a method ofoperating a burner with a plurality of inlets on the front surface areaof the burner to provide combustible gas to a combustor. The methodcomprises dividing the front surface area into a plurality of subareas,and for at least one subarea selecting at least four inlets which areencircling the respective subarea. The method further comprise providingcombustible gas only through the selected inlets such that a gasrecirculation in the combustor is facilitated corresponding to eachsubarea.

The underlying idea here is to provide gas recirculation inside acombustor by providing and operating inlets in at least one subareawhich is smaller than that of front surface area of the burner. Byoperating the inlets encircling the subarea a gas recirculation or gasrecirculations, if more than one subarea are operated, is formed whichcan maintain the sustainable temperature for the combustion. The numberof subareas operated is based on the load of the gas turbine which canalso be directly mapped to the combustor load. Operating the inlets in asubarea or subareas also enables staging the supply of combustible gasto the combustor for combustion. The combustion resulting in thecreating of gas recirculation which is hot thereby resulting inmaintaining the required temperature throughout the entire load range.By operating a single smaller subarea at lower loads, the combustionassociated with that subarea can be sustained. This combustion createshot recirculation which also provides stability to flames in thecombustor provided for the combustion. As the load increases othersubareas can be made operational to supply the combustible gas to thecombustor. Practically, at least four inlets are required to realize agas recirculation in a subarea. The staging of the combustible gasreferred in the invention should also be interpreted as the staging ofthe fuel since the inlets are generally supplied continuous by air inindustrial operations.

According to a preferred embodiment, the burner further comprises apilot inlet in at least one of the subareas. This pilot inlet helps insupplying flames to provide adequate temperature to start the combustionprocess.

In an alternative embodiment, the inlets encircling the subarea arespaced equally. This enables to create a stable recirculation using thecombustible gases injected into the combustor by the inlets in thesubarea.

In another alternative embodiment, the front surface area comprises oftwo or three or more subareas. Having plurality of subareas enables moreflexibility or control of the supply of the fuels to the combustor forcombustion. That means the supply of the fuels to the combustor can bestaged. The more the number of subareas, more the number of staging thatcan be realized. During staging, the amount of combustible gas suppliedthrough the inlets in one or more subareas are regulated or controlledbased on the load of gas turbine. Also simultaneous operation ofmultiple subareas will result in plurality of gas recirculation, whichfurther provides more tuning flexibility regarding thermo acousticoscillations in the gas combustor. Practically two or three gasrecirculations are optimal even though more gas recirculations can berealized for the operation.

In another alternative embodiment, the shape of said burner is circularor elliptical. The shape of the burner enables to arrange the inlets inmultitude of possibilities to get a gas recirculation.

In another alternative embodiment, the subareas formed by thearrangement of the inlets on the front surface area have symmetricalconfiguration. Symmetrical configuration of the subareas andcorresponding inlets arranged will enable to provide more stability tothe combustor, if operated simultaneously.

In another alternative embodiment, the subareas formed by thearrangement of the inlets on the front surface area has asymmetricalconfiguration. This enables the burner to have subareas having differentarea configurations and also possibly with different number of inletsencircling them which further helps in staging the combustible gas byselecting the required subarea based on the combustor load. For exampleif the load is very low, the smallest subarea can be selected for theoperation.

In another alternative embodiment adjacent subareas on the front surfacearea of the burner are adapted to use at least one inlet in common. Thishelps in effective utilization of the front surface area of the burnerto generate effective gas recirculation.

In another alternative embodiment, the inlets arranged on the frontsurface area, to supply the combustible gas to the combustor, are of atleast two different diameters. This will help in the operation of therequired subarea which further regulates the flow of combustible gasbased on the load requirement. For example, at lower loads the inletswith smaller diameter can be operated and at higher loads, when morecombustible gas is required the inlets with larger diameter could beused.

In another alternative embodiment, said burner operates on pre-mixed jetflames. Combustion systems based on pre-mixed jet flames offer specialadvantages over for example, swirl stabilized systems from thethermo-acoustic point of view, owing to the distributed heat releasezones and the absence of swirl induced vortices. By appropriatelyselecting the jet impulse, small scale eddy structures can be createdwhich dissipate the acoustically induced fluctuations of heat release,thereby suppressing the pressure pulsations which are typical for swirlstabilized flames.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described hereinafter with reference toillustrated embodiments shown in the accompanying drawings, in which:

FIG. 1 illustrates an elliptical burner where inlets are arranged in thefront surface area of the burner so as to form two sub areas accordingto an embodiment of the invention,

FIG. 2 illustrates a circular burner where inlets are arranged in thefront surface area of the burner so as to faun multiple sub areasaccording to an embodiment of the invention with a central pilot inlet,

FIG. 3 illustrates a circular burner where inlets are arranged in thefront surface area of the burner so as to form multiple sub areasaccording to an embodiment of the invention with a pilot inlet in one ofthe subareas,

FIG. 4 illustrates a combustion chamber, showing the gas recirculation,when operating multiple subareas in a burner as shown in FIG. 1, and

FIG. 5 illustrates a combustion chamber, showing the gas recirculation,when operating two subareas using a burner as shown in FIG. 3.

DETAILED DESCRIPTION OF INVENTION

It is known that undesired thermoacoustic oscillations frequently occurin combustors of gas turbines. The term “thermoacoustic oscillations”designates mutually self reinforcing thermal and acoustic disruptions.In the process, high oscillation amplitudes can occur, which can lead toundesired effects, such as to high mechanical loading of the combustorand increased NOx emissions as a result of inhomogeneous combustion. Inorder to ensure a high output in relation to pulsations and emissionsover a wide operating range, further tuning of the fuel distribution andactive or passive control of the combustion oscillations may benecessary.

FIG. 1 illustrates an elliptical burner 100, where inlets are arrangedin the front surface area 101 of the burner so as to form two subareas102 and 104 according to an embodiment of the invention. The inlets 105along with the common inlets 106 encircle the subarea 102. Likewise,inlets 107 along with the common inlets 106 encircle the subarea 104.During operation of the burner, i.e. during combustion, a gasrecirculation in the combustor is facilitated or produced correspondingto each subarea 102 and 104 if all the inlets of the burner areoperated. It is to be noted that in this embodiment no inlet is used asa pilot inlet to start the combustion and the inlets encircling thesubarea are substantially spaced at equal distance between them.Piloting could even be realized by a separate burner if required or evenany other heating means can be used to provide the required temperaturefor the start of the combustion.

In FIG. 1, the inlets are placed in the front surface area to form twoalmost identical or symmetrical subareas. The upper subarea 102 and thelower subarea 104 have symmetrical configurations. The number ofsubareas in the FIG. 1 is limited to two, but practically the burnercould be realized by three or more subareas. For example at low loadoperation of the gas turbine, the required combustion temperature couldbe maintaining by supplying the combustible gas, i.e. the fuel and airmixture through the inlets of any one of the subarea 102 or 104. Theinlets in the other subarea will be supplied only with air, resulting ina flame in only one of the two subareas for which the combustible gaswas supplied. The flame will generate a hot gas recirculation. The airflowing through the other subarea also results in a recirculation, whichwill not be hot, but is referred as a cold recirculation here after forthe explanation and understanding.

Also it is possible to merge the subareas during operation. At high loadoperation all the inlets of the burner are used to supply combustiblegas to the combustor. The operation of all inlets in the burner resultsin two hot recirculations; one formed by the inlets of the subarea 102and another formed by the inlets of the subarea 104.

FIG. 2 illustrates a circular burner 200, where inlets are arranged inthe front surface area 201 of the burner so as to form multiple subareas 202, 204 and 206 according to an embodiment of the invention witha central pilot inlet 209. The centralised pilot could be used for anyone or all of the subareas 202, 204 and 206. The placement of the inletsin the front surface of the burner as shown in FIG. 2 provides anasymmetric configuration of the subarea, since for example the number ofthe inlets which encircles each subarea varies. Also it should be notedthat the size, more specifically the diameter of few of the inlets inthe subarea 206 differs from that of the inlets in subarea 202 or 204.Also between adjacent subareas there are inlets which are common. Asshown in FIG. 2, inlet 203 is common to subarea 202 and 204. Likewise,inlet 205 is common to subarea 202 and 206 and also inlet 207 is commonto subarea 204 and 206. As previously mentioned the pilot inlet 209 iscommon to all the subareas. When the load on the gas turbine is low, theinlets in the subarea 202 or 204 is operated and when the load increasesthe inlets in other subareas including the subarea 206 having largerdiameter could be used to supply the combustible gas. Based on the load,different combinations of operation of the subareas are possibleenabling the staging of the combustible gas supply to the combustorthereby resulting in complete combustion throughout the load range andless emissions. Flame stability is also achieved using the hot gasrecirculation formed in the combustion in the combustor. The hotrecirculation formed after the combustion gives enough temperature tosustain the combustion in the region of recirculation resulting in astable flame.

FIG. 3 illustrates a circular burner 300 where inlets are arranged inthe front surface area 301 of the burner so as to form multiple subareas302, 304 and 306 according to an embodiment of the invention with apilot inlet 308 in one of the subarea 306. In the specific arrangement,the pilot inlet can initiate the combustion first and at low loads thesubarea 306 could be operated. As the load increases other subareas canbe made operational by controlling the respective inlets to formmultiple hot recirculations.

FIG. 4 illustrates a combustion chamber, showing the gas recirculation,when using a burner as shown in FIG. 1. FIG. 4 shows a combustionchamber 400, of a can-type combustor. The combustion chamber has aninternal space 402 enclosed by a wall 401, which is generallycylindrical. On the inlet side 403, a burner 404 having plurality ofinlets placed on the front surface of the burner as shown in FIG. 1 isplaced. The burner is considered to be an elliptical burner as shown inFIG. 1. By operating all the inlets in both the subareas the gasrecirculation inside the combustion chamber 400 will be as shown in theFIG. 4, shown by the arrows. The gas recirculation arrows 406 shows therecirculation in the upper region of combustion chamber 400 formed bythe inlets in the subarea 102 of FIG. 1. The gas recirculation arrows407 shows the recirculation in the lower region of combustion chamber400 formed by the inlets in the subarea 104 of FIG. 1. Theserecirculations provide the flame stabilization mechanism. By staging ofthe combustible gas through the inlets, the number of hot recirculationcan be controlled. The number of hot recirculation required can also bebased on the operational load conditions, the required stability andemission requirements.

FIG. 5 illustrates a combustion chamber 500, showing the gasrecirculation when using a burner as shown in FIG. 1. The combustionchamber has an internal space 502 enclosed by a wall 501, which isgenerally cylindrical. On the inlet side 503, a burner 504 havingplurality of inlets are placed. The inlets placed in the front surfaceof the burner are similar to that discussed and shown in FIG. 1. Bystaging the fuel only through one sub area for example, through all theinlets in the subarea 102 of FIG. 1, the gas recirculation inside thecombustion chamber 500 will look like what is shown in FIG. 5. The gasrecirculation arrows 508 show the hot recirculation formed by theoperation of inlets in the subarea 102 and recirculation arrows 506shown in dotted lines indicate the cold recirculation formed by the flowof air through the inlets in the subarea 104. By operating the inlets ina single or inlets in multiple subareas based on the load, the fuelstaging can be achieved and thereby the number of hot recirculationinside the combustor can be controlled for getting flame stability.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternate embodiments of the invention, will become apparent to personsskilled in the art upon reference to the description of the invention.It is therefore contemplated that such modifications can be made withoutdeparting from the embodiments of the present invention as defined.

1. A burner for a gas combustor, comprising: a front surface areadivided into a plurality of subareas; and inlets, arranged on the frontsurface area such that each subarea is encircled by at least four inletsand such that during operation of the burner, a gas recirculation in thecombustor is facilitated corresponding to each subarea.
 2. The burneraccording to claim 1, further comprises a pilot inlet in at least one ofthe subareas.
 3. The burner according to claim 1, wherein the inletsencircling the subarea are spaced equally.
 4. The burner according toclaim 1, wherein the front surface area comprises of two subareas. 5.The burner according to claim 1, wherein the front surface areacomprises of three subareas.
 6. The burner according to claim 1, whereinthe shape of said burner is circular.
 7. The burner according to claim1, wherein the shape of said burner is elliptical.
 8. The burneraccording to claim 1, wherein the subareas formed by the arrangement ofthe inlets on the front surface area has symmetrical configuration. 9.The burner according to claim 1, wherein the subareas formed by thearrangement of the inlets on the front surface area has asymmetricalconfiguration.
 10. The burner according to claim 1, wherein adjacentsubareas on the front surface area are adapted to use at least one inletin common.
 11. The burner according to claim 1, wherein the inletsarranged on the front surface area are of at least two differentdiameters.
 12. The burner according to claim 1, wherein said burneroperates on pre-mixed jet flames.
 13. A method of operating a burnerwith a plurality of inlets on a front surface area of the burner toprovide combustible gas to a combustor, comprising: dividing the frontsurface area into a plurality of subareas; for at least one subarea,selecting at least four inlets which are encircling the respectivesubarea; and providing combustible gas only through the selected inletssuch that a hot gas recirculation in the combustor is facilitatedcorresponding to each subarea.
 14. The method according to claim 13,wherein the combustible gas is provided through at least one inletduring startup of the combustor.
 15. The method according to claim 13,wherein the number of subareas operated during an operation of thecombustor is based on the combustor load.
 16. The method according toclaim 13, wherein the combustible gas supplied through the inlets isstaged based on the combustor load.
 17. The method according to claim13, wherein the subareas formed by the arrangement of the inlets on thefront surface area has symmetrical configuration.
 18. The methodaccording to claim 13, wherein the subareas formed by the arrangement ofthe inlets on the front surface area has asymmetrical configuration. 19.The method according to claim 13, wherein adjacent subareas on the frontsurface area of the burner are adapted to use at least one inlet incommon.